1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device in which an insulating film is formed by irradiating a workpiece with electron beams to cure it.
2. Background Art
Recently, an insulating film is formed by applying a thin-film material on a semiconductor substrate by a spin coating method, etc., and thereafter curing the workpiece. The present inventor etc. have found that characteristics of an insulating film formed of a siloxane material can be improved by irradiating the siloxane material with an electron beam and simultaneously curing it, as disclosed in, for example, U.S. Pat. No. 6,746,969.
When a coated siloxane material layer is irradiated with electron beams and cured, thereby forming an interlayer insulating film, the following advantages can be obtained as compared with a case where a workpiece is only cured without being subjected to irradiation with an electron beam:
1). mechanical strength (hardness) can be improved to about two times that of conventional cases;
2). curing temperature can be decreased from about 400° C. in conventional cases to about 300° C.; and
3). curing time can be shortened from about 30 minutes in conventional cases to about two minutes.
When the aforementioned method is applied to a mask in a resist process, in addition to the above advantages,
4). resistance (selection ratio) of an etching mask can be improved to about two times that of conventional cases.
Recently, a logic LSI has a multilayer process structure including 5 or more layers. In such a case, if an interlayer insulating film material and an etching mask material are separately cured using electron beams, three electron beam irradiation operations are required for each layer (performed when forming an interlayer insulating film, forming a mask in a via hole formation step, and forming a mask in a embedded wiring (damascene wiring) formation step). In a simple curing process using only heat, a batch processing method can be used, in which about 50 semiconductor substrates can be processed at a time. However, if an electron beam irradiation is performed, a so-called single wafer processing method, in which only one semiconductor substrate is processed at a time, should be used. Accordingly, when a curing technique using electron beam irradiation is simply employed to cure each layer, the productivity is degraded, and the manufacturing cost is increased.
With respect to a curing operation by heat, a technique is proposed in which insulating films using two or more different kinds of materials are stacked and simultaneously cured, as disclosed in Japanese Patent Laid-Open Publication No. 2003-289099. In this technique, there is a problem in that when the shrinkage percentages of the layers constituting the stacked layer are considerably different from each other, cracks and layer separations are likely to occur.
Since the miniaturization of semiconductor devices has advanced, thereby decreasing the thickness of interlayer insulating films, it has become difficult to cure such thin interlayer insulating films using electron beam irradiation. In a curing operation using heat, it is possible to uniformly apply heat in a depth direction of the interlayer insulating film. In a curing operation using electron collisions caused by electron beam irradiation, it is necessary to decrease the energy (acceleration voltage) for injecting electrons to the surface of the layers. Otherwise, electrons pass through an interlayer insulating film, thereby adversely affecting layers and gates of transistors formed underneath the interlayer insulating film, and resulting in the degradation of the quality of the entire semiconductor device. For example, when electrons reach a layer located underneath the interlayer insulating film, a defect level is formed in a gate oxide layer, thereby shifting the threshold voltage of a transistor from a predetermined value, and resulting in that it is not possible to obtain desired transistor characteristics.
Furthermore, it is possible that a gas in the atmosphere is changed to a plasma by electron beam irradiation, thereby forming a damaged layer at the top surface of the interlayer insulating film due to the interaction of the plasma and the electrons, resulting in line-to-line leakage issues between wires.